upgrade to alpine 3.8.1 for remote code execution exploit fix

[飞走不可]

Refer to:
Details here,
https://justi.cz/security/2018/09/13/alpine-apk-rce.html
and here
https://alpinelinux.org/posts/Alpine-3.8.1-released.html

[c0b]

are you aware #91 was handled 3 days ago already

[飞走不可]

so sorry. I forgot to check the issue before. 🤦‍♂️
thanks. 👍

[飞走不可]

please close this issue. thank you

[c0b]

duplicate of #91